Field of the Invention
This invention relates to a hydrostatic drive with a hydrostatic pump driven by a drive motor and connected in a closed circuit with a hydrostatic motor. The hydrostatic motor is in a drive connection with the consumer. The closed circuit is formed by a first hydraulic connection and a second hydraulic connection. Each of the hydraulic connections can form the high-pressure side or the low-pressure side of the closed circuit. A high pressure accumulator device can be connected with the respective high-pressure side hydraulic connection for the storage of energy and the discharge of energy and, simultaneously, the respective low-pressure side hydraulic connection can be connected with a hydraulic balancing device. A valve device is provided for the control of the simultaneous connection of the high pressure accumulator device with the high-pressure side hydraulic connection and the hydraulic balancing device with the low-pressure side hydraulic connection.
Description of Related Art
Hydrostatic drives in a closed circuit are used for driving a consumer in vehicles such as motor vehicles or public transit vehicles, e.g. buses, preferably for urban mass transit, and for mobile self-propelled machines, in particular industrial trucks, agricultural machines, forestry machines and construction machines, such as, for example, excavators, wheel and telescoping loaders, tractors, combine harvesters, forage harvesters, sugar beet and potato harvesters.
With the high pressure accumulator device for the storage and discharge of energy and which can be connected with the respective high-pressure side hydraulic connection of the closed circuit, a hybrid drive and, thus, a hybrid function, can be realized in a hydrostatic drive with a closed circuit. With the energy in the high pressure accumulator device, during a discharge operation of the high pressure accumulator device, the consumer can be driven in a drive phase. If the high pressure accumulator device is operated in a charging operation during a braking or deceleration phase of the consumer and is charged with hydraulic fluid, energy can be recovered during the braking or deceleration of the consumer.
In a hydrostatic drive in a closed circuit, it must be ensured that during the charging operation of the high pressure accumulator device in which a determined amount of hydraulic fluid is removed from the high pressure accumulator device out of the high pressure hydraulic connection of the closed circuit, the corresponding quantity of hydraulic fluid is made up at the low-pressure side hydraulic connection of the closed circuit. During discharge operation of the high pressure accumulator device, in which a determined quantity of hydraulic fluid is fed from the high pressure accumulator device to the high pressure side hydraulic connection of the closed circuit, it must be ensured that the corresponding quantity of hydraulic fluid is removed from the low-pressure side hydraulic connection of the closed circuit.
To make possible this balancing in terms of quantity or volume at the low-pressure side hydraulic connection of the closed circuit during the extraction or the addition of a quantity of hydraulic fluid at the high-pressure side hydraulic connection by the high pressure accumulator device, a hydraulic balancing device can be provided that balances the amount or volume at the two hydraulic connections of the closed circuit by a discharge or addition of hydraulic fluid at the low-pressure side hydraulic connection.
If, on a hydrostatic drive system with a closed circuit, each of the two hydraulic connections can form the high-pressure side or the low-pressure side and the hybrid function is to be made available regardless of which of the hydraulic connections represents the high-pressure side and the low-pressure side, a valve device for the hybrid function is necessary that makes possible the simultaneous connection of the high pressure accumulator device with the respective high-pressure side hydraulic connection and the hydraulic balancing device with the respective low-pressure side hydraulic connection.
DE 10 2007 012 121 A1 describes a generic drive system with a hybrid function in which the valve device that makes possible the simultaneous connection of the high pressure accumulator device with the respective high-pressure side hydraulic connection and the hydraulic balancing device with the respective low-pressure side hydraulic connection is formed by an electrically actuated directional control valve or by a plurality of individual valves that can be pre-set with one or more electrically actuated setting valves. On account of the requirement for the electric actuators, however, the electric actuation or electric setting of the valve device results in a high level of construction effort with high manufacturing costs. The valve device takes up a large amount of space and is prone to interference and malfunctions.
Therefore, it is an object of this invention to provide a hydrostatic drive in which the valve device for the hybrid function has a simple, compact, and economical construction as well as a robust operation.